1. Field of the Invention
This invention relates in general to apparatus used in the drilling of oil and gas wells. In particular, the invention relates to remotely controllable safety valves for controlling flow through rotatable tubular members and means for manually controlling the valve by a remote power source.
2. Description of the Prior Art
During modern rotary drilling operations, drilling mud is pumped from the mud pumps at the drilling platform, through the swivel, the rotating kelly, and the rotating drilling string, in order to sweep or wash away cuttings from the drilling bit and return them via the annulus between the string and the well bore to the surface in a manner well known. In the event of a sudden increase in downhole pressure, such as from a kick, or when a blowout threatens, upward flow through the drilling string and kelly from downhole must be blocked in order to maintain control of the well and prevent drilling mud loss.
Often, valves are mounted above and below the kelly in order to shut off flow through the kelly and the drilling string. Such valves, sometimes referred to as "kelly cocks", have been designed to be manually rotated to a closed position by a special tool.
Occasionally, it is necessary to close off flow through the kelly under emergency conditions such as, for example, the occurrence of an offshore platform fire. In such an emergency situation, it may be impossible for an operator to physically be close enough to the kelly cock to close the valve manually. Thus, the well continues to flow until it can be shut in by other means which can be costly to the ecology of the area and costly economically. In addition, under blowout or downhole increased pressure conditions it may be impossible to close the kelly cock because of gases, danger of fire or other reasons.
U.S. Pat. No. 3,941,348 to Mott, one of the inventors of the present invention, discloses a remotely operable safety valve mounted between the swivel and the kelly in drilling operations including a spherically-shaped valve element which is mounted in a generally tubular housing rotatable with the swivel sub, the kelly and the drill string. Hydraulic means move the valve element between open and closed positions in order to control flow through the drill string and prevent in-line blowouts. As an additional safety feature, spring means move the valve element to a closed position in the event of a failure of the hydraulic means.
It is an object of the present invention to provide an improved safety valve to that disclosed in the above mentioned patent.
It is another object of the invention to provide a safety valve having automatic centering of cam follower bearings between two operating positions to prevent wear of the bearings that would otherwise occur if they were constantly bearing against an actuating surface as the kelly rotates.
Still another object of the invention is to provide for manual operation of the valve if the remote power source normally controlling the valve were to fail.